Santorum and Bachmann, two candidates who on paper seem right up Iowa's alley, have so far spent much more time campaigning there than anyone else in the field but without much to show for it in Iowa polling, which instead has tracked with national polling with Cain, Romney and Gingrich in front. Iowa's importance was established when Jimmy Carter used it to surprise the field and get momentum and national press. But those days are over. The races get massive media exposure beginning over a year before they start. Iowa is less the 1st contest than the 50th with the US being the first 49. And actually, the small sample of people in any polls has more disproportionate influence than Iowa caucus-goers. Do media-devoured and -regurgitated national polls and analysis in the run up to Iowa dictate candidate momentum that Iowa follows more than Iowa dictates subsequent national polling? Is there any recent case where the top finishers in Iowa were out of sync with national polling that closely preceded it? The case that jumps out is John Kerry and Howard Dean. Iowa definitely changed the trajectory of that primary season but weren't Kerry and Edwards still surging in national polling ahead of Iowa? And it's impossible to measure the effect the Iowa results themselves as opposed to the media's orgasm over the "Dean Scream" which, while largely a myth, was covered as much or more than Rick Perry's "Oops".

There's no excuse why one state should have that much influence over the Presidential selection process. Full stop. That Iowa (and New Hampshire as well) lacks the whole nation's diversity is another compunding problem. And they have tried to address it in the most half-assed way possible, by giving SC and NV second billing. I honestly don't know why either political party doesn't move to national primary. It would be great spin to say "My party thinks that every American ought to have equal vote. Evidently, the other doesn't."

I honestly don't know why either political party doesn't move to national primary.

Even if they wanted to do a national primary, how would they make it happen? Iowa and NH (and some other states too) would just move their primaries up before the national primary. 2008 and 2012 showed that the national parties' ability to control the calendar is limited. You would need to have federal legislation to make it happen, so that a court can order that the primaries happen on such-and-such a date: